1. Field of the Invention
The present invention relates to a communication apparatus that performs communication over an IP (Internet Protocol) network and a data transmission method of the communication apparatus.
2. Description of Related Art
Conventionally known methods of facsimile communication via a network, such as the Internet and the like, include a method for transmitting image data as a file attached to e-mail based on SMTP (Simple Mail Transfer Protocol) (ITU-T T.37 standard); a method for transmitting packetized G3 facsimile modem signals on a real-time basis (ITU-T T.38 standard); and a method for transmitting G3 facsimile modem signals as they are as audio signals (pass-through method). While being able to ensure a highly reliable communication, however, the T.37 standard is inferior in real-time performance. Meanwhile, the T.38 standard, which has a superior real-time performance, is complex in processing since the standard follows ITU-T T.30 procedures. Further, the pass-through method is highly versatile since the method handles modem signals as if they are audio signals, but communication may be unstable as being affected by packet loss, delay, and the like.
Recently, SIP (Session Initiation Protocol) is used as a signaling protocol in IP telephones, video-phones, and the like. SIP enables transmission and reception of audio, image, video, and the like in a relatively simple process while maintaining the real-time performance. As technology of this type, a data transfer apparatus is known, for example, in which two apparatuses that exchange the capability with each other, in a call control process, via the SIP messages containing the capability information including the type of the codec and the like of a source apparatus is added, and then transfer audio, image, and the like in a communication process (Refer to Related Art 1).
[Related Art 1] Japanese Patent Laid-open Publication No. 2005-150830
However, the conventional technology described in Related Art 1 above, which transmits and receives data based on RTP (Real-time Transport Protocol) prioritizing real-time performance, is lack in the communication stability. Further, the technology does not meet a request such as to handle received data as a file on a receiving side. In transmission and reception of image data, in particular, it is difficult to surely transmit a predetermined number of pages of facsimile images and output the images on the receiving side, as conventional G3 facsimile apparatuses do.